The present invention relates to an apparatus for generating two-dimensional and/or three-dimensional objects. In particular, the present invention relates to holographic two-dimensional (2D) and/or three-dimensional (3D) displays as well as to display and imaging applications which use segmented illumination and/or segmented imaging. In particular, the present invention refers to combining of a plurality of light sources.
Holographic display devices require a light source or an illumination device that emits sufficiently coherent light. The illumination device or light source should achieve a high power at stabilized wavelength. Such illumination devices or light sources are at a very high price.
Therefore, devices able to combine several light sources, for example lasers, and to enable high definition (HD) holographic display products are of special interest. Important criteria or roles are the price and the total optical power of the light sources, which might exceed a value of 1W per primary color, for example, for a 40 inch holographic display device if an outdoor application or a head-up display (HUD) within a mobile vehicle might be the intended application. In addition, a segmented illumination and/or a segmented imaging would allow effective local dimming which enables a high dynamic range (HDR) of images generated in a three-dimensional object space. And, it also allows an effective power management by increasing the total power efficiency of an imaging apparatus, that is, of a display device as, for example, a holographic television (TV).
Local dimming enables a high dynamic range and a high image contrast. A segmented illumination or a scanning illumination may be able to provide a homogeneous illumination of a spatial light modulator device (SLM), which is used for an image generation, or for a local dimming-type of illumination. Such a local dimming-type of illumination is an intensity distribution that can have, for example, intensity values ranging from 0 (zero) to 1 (one), where it is referred to a maximum intensity value obtained locally. For example, in a two-dimensional (2D) display device the spatial light modulator device, which has to be illuminated, is equivalent to the plane of the image points generated. In holographic display devices, these two planes are not the same. Holographic display devices require a different approach, especially, in order to provide high definition (HD) imaging in combination with segmented illumination.
In other words, local dimming based on scanning of a single light beam, which has e.g. a diameter of 1 mm, might be used for a high definition two-dimensional display device. But using this approach in order to illuminate the spatial light modulator device generating a three-dimensional (3D) holographic scene will result in a low resolution of the image obtained. Holographic display devices require tailored illumination.
A segmented decoupling of light out of a light guide is disclosed in WO 2003/081320 A1. These decoupled wave field segments representing a two-dimensional object plane are redirected to the eyes of an observer. This document discloses a plurality of embodiments using segmented illumination or segmented decoupling of light. The segmented illumination is provided in the plane of a spatial light modulator which is the plane the observer is looking at. In this specific case high definition viewing experience can only be achieved partially. In detail, the document to WO 2003/081320 A1 discloses an optical device including a light-transmitting substrate having at least two major surfaces and edges. The optical device comprises further optical means for coupling light into the substrate by total internal reflection and at least one partially reflecting surface located in the substrate, where this surface is non-parallel to the major surfaces of the substrate. The light beams coupled into the substrate have the same off-axis angle inside the substrate and intersect the partially reflecting surface with two different incident angles. However, a high definition (HD) resolution cannot be provided and achieved using such a device.